Centrifugally actuated clutches are well known for driving many different mechanisms. A particularly useful class of centrifugal clutches has an idle region in which the clutch shoes are restrained out of contact with a driven clutch drum over a desired range of drive motor rotational speed. Typically, the major factors determining the idle range are the center of gravity and/or mass of the clutch shoes, connection of the clutch shoe to the driven supporting structure, and the nature and strength of the generally inwardly directed restraining forces.
Typically, in applications wherein a larger idle range is necessary, either the structure or mass of the clutch shoes or the strength (usually the spring constant) of the clutch shoe restraining force is changed. Thus by either reducing the effective centrifugal mass of the clutch shoes or by increasing the restraining force, a larger rotational speed is required to effect shoe movement, and a larger idle speed range is obtained. In many applications, however, it is impossible or undesirable to alter the structure of the clutch shoe assembly and hence it is only the restraining force which can be changed. However, the restraining force is generally provided by spring materials, which can be used only over certain well known ranges, past to top limits of which, they become overstressed and hence unreliable.
A particularly, commercially successful, construction of the centrifugal clutch mechanism is one which uses a circumferential coiled spring to provide the restraining force. These mechanisms have been the subject of many patents and various means have been devised for either improving the coiled spring construction or replacing it with, for example, solid springs such as those described and claimed in Frederickson, U.S. Pat. No. 3,768,611, issued Oct. 30, 1973. Although these systems have in general proven to be of considerable commercial impact, they too meet serious obstacles as the idle range is increased.
It is therefore a principal object of the invention to provide a centrifugal clutch mechanism having an increased idle range without the inherent disadvantages of spring material overstressing. Other objects of the invention are to provide a centrifugal clutch mechanism which is reliable, simple in construction, substantially rattle-free, strong, and relatively low in manufacturing cost.
A further object of the invention is to provide a centrifugal clutch mechanism in which the component parts are positionally stable.